feat: AI model selector + i18n nav labels (RU/EN) on new modules

AI model selector:
- AiAssistantService::MODEL_DEFAULTS and MODEL_OPTIONS const tables (3 picks per
  provider: Claude Opus 4.7 / Sonnet 4.6 / Haiku 4.5, OpenAI 4o / 4o-mini,
  Gemini 1.5 Pro / Flash). Default upgraded from Sonnet 4.5 → Sonnet 4.6.
- modelFor(provider, company?) resolves tenant override > global default.
- All 8 hardcoded model strings replaced with modelFor() across callClaude
  (chat with tool-use), callOpenAI, callGemini (chat), postClaude/postOpenAI/
  postGemini (single-shot), and OcrInvoiceService.
- Settings page adds 3 model selectors per provider with persistence at
  settings.ai.models.{claude,gpt,gemini}.

i18n nav labels:
- TireSet / Bodyshop / Subcontractor / SubcontractJob / PricingCoefficient /
  ShopCustomer resources: getNavigationLabel / getNavigationGroup /
  getModelLabel / getPluralModelLabel return __()-wrapped strings.
- 20 keys added to lang/ru.json and lang/en.json.

Tests (4 new): default model, tenant override wins, unknown provider falls
back to claude default, options dictionary contains each default key.

Full suite: 134 passed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lang/en.json

@@ -21,7 +21,6 @@
     "Status": "Status",
     "Actions": "Actions",
     "Notifications": "Notifications",
-
     "Clienți": "Clients",
     "Mașini": "Vehicles",
     "Cereri": "Leads",
@@ -53,5 +52,25 @@
     "Jurnal": "Audit log",
     "Telefonie": "Calls",
     "Finanțe": "Finance",
-    "Site PSauto": "Public site"
+    "Site PSauto": "Public site",
+    "Seturi anvelope": "Tire sets",
+    "Anvelope": "Tires",
+    "set anvelope": "tire set",
+    "seturi anvelope": "tire sets",
+    "Tinichigerie / Detailing": "Body / Detailing",
+    "Tinichigerie": "Body shop",
+    "lucrare caroserie": "body job",
+    "lucrări caroserie": "body jobs",
+    "Subcontractori": "Subcontractors",
+    "Subcontractare": "Subcontracting",
+    "subcontractor": "subcontractor",
+    "Lucrări terți": "Outsourced jobs",
+    "lucrare terți": "outsourced job",
+    "lucrări terți": "outsourced jobs",
+    "Coeficienți preț": "Pricing coefficients",
+    "coeficient": "coefficient",
+    "Magazin": "Shop",
+    "Clienți magazin": "Shop customers",
+    "client magazin": "shop customer",
+    "clienți magazin": "shop customers"
 }